The owner will decide what is required insurance for renters. Personally, I would not rent an airplane without renter's insurance. Often owners will state in the rental contract that the deductible for their loss insurance is the responsibility of the renter. To keep costs down, they can have large deductibles, sometimes $10k or more. So unless you are prepared to write a $10k check in the event of an accident or incident, I would renew that policy.